diff --git a/tableauserverclient/server/request_factory.py b/tableauserverclient/server/request_factory.py
index 31c204110..fdc799af1 100644
--- a/tableauserverclient/server/request_factory.py
+++ b/tableauserverclient/server/request_factory.py
@@ -363,7 +363,7 @@ def _generate_xml(self, workbook_item, connection_credentials=None, connections=
         if workbook_item.show_tabs:
             workbook_element.attrib['showTabs'] = str(workbook_item.show_tabs).lower()
         project_element = ET.SubElement(workbook_element, 'project')
-        project_element.attrib['id'] = workbook_item.project_id
+        project_element.attrib['id'] = str(workbook_item.project_id)
 
         if connection_credentials is not None and connections is not None:
             raise RuntimeError('You cannot set both `connections` and `connection_credentials`')